This invention relates generally to voice conferencing devices and, more particularly, is concerned with a digital voice conferencer (DVC) which provides digitally encoded vocal communication among a plurality of remotely located digital voice terminals which typically achieve bit rates between 2.4 to 32 kilobits per second. Examples of voice digitizers that can be utilized in conjunction with the conferencer of the present invention include linear predictive coders (LPC), vocoders, adaptive differential pulse modulators (ADPCM) and delta modulators such as continuously variable slope delta modulators (CVSD). The LPC, vocoders and ADPCM digitizers all generate a predetermined length of data sequences and are typically characterized as "framed" digitizers. The delta modulators generate no such predetermined data sequence length and are accordingly characterized as "unframed" digitizers.
Former digital voice conferencing techniques involving more than two people using such voice digitizers involved the individual conversion of the transmitted digital sequences from each terminal back to an analog form at some central conferencing location. The set of resultant analog waveforms were then converted into a single analog waveform either by a voice-actuated switch or by a waveform summing process. The single resulting analog waveform is then re-digitized by a voice digitizer and redistributed to each of the conferees. This process of first converting to analog, then re-digitizing, considerably degrades the quality of the conference. Such operations and conversions are avoided in the structure and function of the present invention, thereby providing a corresponding improvement in conferencing quality.